The preparation of uncured elastomer for use in manufacturing tires, hose, belts and other articles of reinforced or unreinforced elastomer requires that the elastomer have various substances incorporated therein to provide desired properties both during processing and in the final product. This is customarily effected by adding the various ingredients to the elastomer as it is mechanically worked. Due to the nature of some of the ingredients, and/or the effect they have on the composition, all the ingredients generally cannot be added at the same time. Consequently, it is customary to subject the elastomer to mechanical working, as by means of a Banbury mixer or other mixing apparatus, with the several ingredients added at various times during that mixing. The time of addition of the ingredients is determined, in some instances, by the temperature of the mix and/or by the length of time the materials in the mixer have been subjected to working. There also have been attempts to determine the proper times to add ingredients by the amount of power that has been consumed by the mixing apparatus. Unfortunately, however, none of the systems customarily employed have been entirely satisfactory.
The use of temperature as the criterion of the amount of working before adding ingredients is inexact due in large measure to the difficulty of accurately measuring the temperature of the mixture during the operation. Likewise, the addition of ingredients in accordance with the length of time mixing has occurred has not proved satisfactory since various elastomers respond differently to mixing and small differences in timing can be significant. Furthermore, in some instances, the addition of one ingredient may alter the length of time of mixing that should be required before the addition of another ingredient. Hence, it is practically impossible to develop a meaningful time control for the addition of ingredients.
The efforts to regulate the addition of compounding ingredients to elastomers by the amount of power consumed by the mixing apparatus has heretofore proved unsatisfactory since available meters have not been sufficiently accurate for the time periods which are of interest in such operations. Also such instruments are not resettable or readily controlled for starting and stopping when a batch is introduced into or removed from the mixing apparatus. Moreover, there has been no readily available means to eliminate from the readings of conventional instruments the power consumed by the apparatus in frictional and other losses.
The inability to accurately determine the proper intervals at which compounding ingredients should be added to elastomer has resulted in substantial variations in the nature of separately mixed batches with corresponding lack of uniformity and predictability of characteristics of products made therefrom. Similar difficulties are encountered in attempting to secure uniformity of other elastomer processing operations such as conventional warm-up or other conditioning operations preparatory to employing the elastomer in extruding, calendering and similar operations.